1. Technical Field
The present invention relates to a pulse wave analyzer that analyzes pulse wave signals and a blood pressure estimating using the pulse wave analyzer.
2. Related Art
It is known that a cuff is used in general in measuring a blood pressure. However, use of a cuff raises a problem of giving feeling of pressure to the examinee due to the inflation of the cuff or a problem of disabling continuous measurement of blood pressure.
In this regard, recently, a different measurement technique is under development. In this measurement technique, pulse wave signals are analyzed to obtain a pulse wave velocity, feature points of pulse waves, and the like, for the calculation of a blood pressure (refer to JP-A-H10-295656, JP-A-H10-295657, JP-A-H11-318837, JP-A-2003-000555, JP-A-2001-008907, JP-A-2006-263354, JP-A-2007-082682 and JP-A-2008-302127). For example, volume pulse waves can be measured using light and thus the size of the device for the measurement can be reduced. In addition, use of measurement of volume pulse waves can eliminate the oppression given to the examinee and enables continuous measurement of blood pressure.
For example, in order to extract information from pulse wave signals, the waveforms are doubly differentiated. However, such a differentiation raises a problem of allowing the waveforms to be easily affected by disturbance. To take measures against this, pulse wave signals are averaged before being differentiated so that the pulse wave signals are cleaned (so that a high S/N ratio is obtained) (see JP-A-H05-312962 and JP-B-3965435).
In averaging pulse wave signals, the pulse wave signals are segmented and cut off on a beat-by-beat basis. To this end, base points of the segment are required to be determined. The techniques disclosed in JP-A-H05-312962 and JP-B-3965435 suggest use of differential peaks or double differential peaks of pulse wave signals as the base points for averaging. However, when large disturbance is caused, these peak positions cannot be detected with high accuracy. As a result, the accuracy in cut-off intervals of the pulse wave signals is lowered, and thus the effect of averaging is not well exerted, or the addition carried out in the averaging is likely to cause further disturbance in the waveforms of the pulse wave signals.